The orientation of a reference trihedron tied to the body of a satellite can be controlled about three axes by a cluster of at least three gyroscopic actuators whose gimbal exhibits just one axis of orientation of the axis of the wheel; two gyroscopic actuators suffice for 2-axis control. In practice, in general at least four gyroscopic actuators are used in a cluster to ensure redundancy for 3D control. A particularly advantageous example of an attitude control system using gyroscopic actuators is given in patent FR 98 14548 or U.S. Pat. No. 6,305,647 to which reference may be made.
Most existing gyroscopic actuators have an architecture of the kind shown diagrammatically in FIG. 1. The gyroscopic actuator comprises a plinth 10 intended to be fixed to the body of the satellite. It can moreover define, with a leaktight envelope (not represented), a volume in which the active part of the actuator is placed. Mounted on the plinth is a wheel support 12 that a motor can orient on the plinth about an axis z. Hereinafter the term “wheel” 14 will designate an assembly which comprises a part secured to the support and a spinner that can rotate on the support about an axis x orthogonal to the axis z of rotation of the support. An electric motor drives the wheel, generally at constant and regulated speed.
The support, that is generally referred to as a gimbal, although it can only orient the axis of the wheel about a single axis, generally exhibits an annular shape centered on the z axis. It completely surrounds the wheel or spinner. Consequently, the assembly occupies a considerable volume and has a high mass for given maximum angular momentum and rigidity. Now, due to the constraints encountered on board a satellite, the space required for the gyroscopic actuators and their mass must be reduced as much as possible for given angular momentum capacity.